Full-duplex operation is a promising manner in which to increase throughput of wireless systems. For example, in the media access control (MAC) layer, the full-duplex operation can be used to increase the efficiency of random access. A wireless access point (AP) utilizing full-duplex mode may communicate with several wireless devices. If two or more devices transmit data to the AP at the same time on the same channel, the data from both wireless devices is undecipherable by the AP. In this situation, neither wireless device is successful in its data transmission. To avoid this scenarios, may wireless systems utilize carrier sense multiple access (CSMA) collision avoidance (CA) in which the various wireless devices use carrier sensing to avoid collisions by transmitting only when the channel is sensed to be “idle.” However, even using CSMA/CA, collisions sometimes occur due to the hidden node problem.
FIG. 1 is a block diagram of a wireless network 100 illustrating the hidden node problem. Wireless network 100 includes an AP1 104, a first wireless station (STA1) 102 and a second STA2 106. STA1 102 is a hidden node from STA2 106. AP1 104 can detect transmissions from STA1 102 and STA2 106, but STA2 106 cannot detect transmissions from STA1 102. In other words, STA2 106 is in the range of AP1 104, but is out of range of STA1 102. Since STA2 106 cannot detect the transmission from STA1 102, STA2 106 may transmit at the same time as STA1 102. When this happens, AP1 104 is unable to decipher the data sent by either STA1 102 or STA2 106. Thus, hidden nodes cause CSMA efficiency (i.e., approximately 90% channel efficiency) to deteriorate to the ALOHA efficiency (i.e., approximately 18% channel efficiency).
One existing solution to the hidden node problem is request-to-send (RTS), clear to send (CTS). FIG. 2 is a block diagram of a wireless network 200 illustrating an RTS-CTS solution to the hidden node problem. Wireless network 200 includes an AP1 204, a first STA1 202, and a second STA2 206 similar to network 100. To solve the hidden node problem, STA1 202 transmits an RTS1 to the AP1 204. The AP1 204 then transmits a CTS1 which the STA2 206 overhears. The STA2 206 sets-up a “virtual carrier sensing” timer to disable its transmission during the transmission from the STA1 202 to the AP1 204. However, although the RTS-CTS mechanism solves the hidden node problem, it is inefficient due to its overhead. Furthermore, if full-duplex is implemented over the entire bandwidth (with a single channel), CSMA does not work since a station overhearing the signal has no idea if it is from the AP or another STA.